It is known that it is particularly important for the crew of an aircraft to be warned as early as possible of a fire breaking out on board, in particular in unpressurized zones of the aircraft that are some distance apart, such as the engines carried by the wings, the main landing gear bay disposed in the intermediate part of the fuselage or the bay of the auxiliary power unit provided in the rear part of said fuselage.
For this purpose, aircraft are equipped with a centralized system for monitoring said zones comprising electrical detection devices respectively disposed in said zones, as well as means for processing the detection signals emitted by said detection devices and alarm means actuated by said processing means, said processing and alarm means being disposed in the vicinity or in the cockpit, that is to say at a location some distance from said detection devices.
The detection devices comprise fire detectors of known types, for example pneumatic or thermoresistive (more particularly with a negative temperature coefficient), disposed in pairs for detection redundancy purposes. Moreover, to limit the number of links between the detection devices and the processing means (and hence to save weight in terms of conductors) and also to limit the number of said processing means, each detection device comprises only two output channels and, in each pair of detectors, one of said detectors is connected to one of said channels while the other detector is connected to the other channel. Thus, said output channels are independent of one another and in the case of a plurality n of pairs of detectors in a detection device (n being an integer different from zero), there are n detectors arranged in parallel and connected to an output channel and n detectors, also arranged in parallel, but connected to the other output channel.
Moreover, said processing means consist of a set of individual computers, each of which is associated with a monitored zone and receives the information conveyed by the two independent channels of the detection device disposed in said zone. Thus, said computer associated with a zone can permanently compare the information that it receives from said two independent channels, and in particular when one of the channels conveys information regarding fire in the zone considered, said associated computer can verify this information by comparing it with that transmitted by the other channel and determine whether it does or does not have to transmit an alarm signal to said alarm means.
It will be noted that such a manner of operation requires each computer of the processing means to comprise two independent elementary computers (boards) electrically isolated from one another, thereby complicating the structure thereof and increasing the cost thereof.
Moreover, these known monitoring systems are disadvantageous as regards weight and costs, since they require a computer (double) per monitored zone. Thus, if the number of monitored zones is equal to six, twelve elementary computers have to be provided.